1. Field of the Invention
The present invention relates to circuits for radio frequency transmitters, receivers, and transceivers, and particularly to a fully integrated DC offset compensation servo feedback loop utilizing R-2R resistance elements that corrects for an unwanted DC component that may be mixed with signals in the transmitter, receiver, or transmitter.
2. Description of the Related Art
Bioinformatics institutes, which host large public collections of molecular biology databases, rely on fast and secure transmission of large amounts of biological data between their servers and their many partners around the world. Some of these partners may be in remote areas, forcing them to employ wireless data transfer. Also, the design of high-quality implantable miniature devices to transmit real-time physiologic parameters from a patient's body to a bioinformatics server is another important task for wireless communications. Such implantable devices are expected to deliver a high level of comfort, mobility, and better patient care. In order to replace the low-frequency inductive coupling techniques in implantable devices, the U.S. Federal Communication Commission (FCC) has recently assigned the 402-405 MHz band with 300 kHz bandwidth channels for medical implant communication service.
This band is expected to facilitate full integration, reduce power consumption, enhance data transfer, and support longer communication range. Also, the metrological aids service has a primary allocation at the 402-405 MHz band for medical implants. In addition, it has a secondary allocation at 402-403 MHz for the Earth exploration-satellite service, together with the metrological-satellite service.
In fact, penetration loss increases with higher frequencies, but it facilitates high-level integration. Fortunately, the penetration loss at these frequencies is relatively insignificant (10 dB with 10 mm tissue penetration), and hence it is inherently compatible with medical implant devices. Also, operation in this frequency range, unlike lower frequencies, promotes small antenna design. The availability of the 402-403 MHz band, internationally accompanied with these advantages, makes this frequency band an attractive choice for the future of medical implant devices.
The use of wireless transmission of biological data between servers and partners and the design of a high-quality implantable miniature devices to transmit real-time physiologic parameters (e.g., ECG, EEG, EOG, EMG, Neural, Blood Flow, Blood Pressure, etc.) from a patient body could be the key point in saving the patient's life. Such implantable devices are expected to deliver a high level of comfort, mobility, and better patient care. The transceivers in such devices often suffer from a DC offset problem, which could reduce the overall dynamic range and even saturate systems at high gain levels. Adaptive digital signal-processing techniques, along with digital-to-analog converters (DAC's), which are typically used in wireless communications, may not be adopted in biomedical applications due to power inefficiency.
Thus, a fully integrated DC offset compensation servo feedback loop solving the aforementioned problems is desired.